Carbonic Anhydrase Polymorphism Reveals Striking Genetic Diversity and Strong Selection Signatures in Nigerian Indigenous Cattle Breeds

Introduction:

Cattle production underpins Nigeria's agricultural economy and rural livelihoods, with over 20 million indigenous animals adapted to harsh environments. However, genetic erosion from cross-breeding threatens these resources. Blood protein polymorphisms like carbonic anhydrase (CA) offer a cost-effective marker for diversity assessment, revealing adaptation and selection patterns. This study characterised CA polymorphism in four key Nigerian breeds—White Fulani, Red Bororo, Sokoto Gudali, and Kuri—to inform conservation and breeding strategies.

Methods:

Blood samples (5 mL) were collected from 351 healthy cattle (121 White Fulani, 97 Red Bororo, 100 Sokoto Gudali, 33 Kuri) across southwestern Nigeria. Erythrocytes were lysed and analysed via cellulose acetate electrophoresis (pH 5.6, 200 V, 45 min). Allele/genotype frequencies were calculated by direct counting, and the Hardy–Weinberg equilibrium (HWE) was tested via χ² and G². Diversity metrics (Shannon’s I and Nei’s heterozygosity), F-statistics, genetic distances (Nei’s test), and neutrality (Ewens–Watterson test) were computed using POPGENE 1.32.

Results:

Two co-dominant alleles (A, B) and three genotypes (AA, AB, BB) were detected. Allele B predominated in White Fulani (0.926) and overall (0.667), while A was highest in Kuri (0.697). Only White Fulani met HWE (P = 0.057); others showed severe heterozygote deficits (e.g., Sokoto Gudali observed AB = 1 vs. expected = 50; P < 0.001). Diversity was highest in Sokoto Gudali (ne = 1.990, I = 0.691, Nei = 0.498) and lowest in White Fulani (ne = 1.220, I = 0.325, Nei = 0.180). FST = 0.191 indicated moderate differentiation; Red Bororo and Sokoto Gudali clustered closely (I = 0.982). The Ewens–Watterson test suggested selection occurred in all three breeds considered in this study.

Conclusions:

CA polymorphism highlights breed-specific diversity and selection pressures in Nigerian cattle, underscoring the need for targeted conservation of unique lineages like Kuri. These findings support sustainable genomics-informed breeding for climate-resilient livestock.